This invention relates generally to hermetic refrigeration compressors of the type used in household appliances, and more particularly to suction muffler and cylinder head arrangements for such compressors, together with arrangements for expediting the assembly of such compressors.
One type of compressor used for household appliances such as refrigerators and freezers utilizes a single piston reciprocating in a cylinder and driven through a crankshaft which is connected directly to the stator of an electric motor. The compressor cylinder block and electric motor are resiliently mounted on springs within the closed steel casing, which is completely sealed except for the conduits carrying refrigerant to and from the interior of the casing. Such compressors have relatively small fractional horsepower electric motors generally operating at a speed of around 3450 rpm when operating from a 60 Hertz supply, and generally range between one-third and one-sixth horsepower. Such compressors must operate at very high efficiency and produce a minimum of noise when installed in the appliance, since such appliances are normally located in the kitchen or other frequently used room in the home.
Because of the size and operating speed of such compressors, valving to admit refrigerant to the pumping cylinder and allowing its discharge is generally in the form of reed valves formed from thin sheets of spring steel operating to cover and uncover ports extending through a valve plate which extends across the open end of the compressor. In many prior designs, the valve plate is covered by a cylinder head generally made from metal for strength which incorporates within the single cylinder head separate plenum chambers or openings for both the suction and discharge sides of the valving which is mounted directly on the valve plate.
In order to ensure quiet operation of the compressor, acoustic mufflers are provided for both the suction and discharge sides, so that the refrigerant pumped by the compressor enters the discharge plenum, from which it passes through a discharge muffler through suitable connection tubing, to the exterior of the casing. Likewise, the incoming refrigerant which may be allowed to flow freely through the interior of the casing is directed through a suction muffler, from which it passes to the suction plenum in the cylinder head.
While older compressor designs used the incoming refrigerant to cool the compressor, and therefore tried to ensure flow of the incoming refrigerant around the various portions of the compressor mechanism before it entered the suction muffler, such heating of the refrigerant results in reduced overall compressor efficiency. For this reason, modern compressor designs try to prevent all unnecessary heating of the incoming refrigerant so that it is as cool as possible when it finally enters the pumping cylinder through the suction valve.
In order to prevent this heat transfer to the incoming refrigerant on the suction side, it has been proposed to make the suction muffler of a suitable thermal insulating material such as a plastic, rather than using metal, which has a much higher thermal conductivity. Furthermore, since one of the sources of heat is the gases on the discharge side, it has been proposed to separate the cylinder head into two separate members, with the discharge plenum comprising one cylinder head and being made of metal for purposes of strength because of the high pressures within this plenum, and the suction side cylinder head forming the suction plenum can be made from a suitable plastic material and combined with portions of the suction muffler. One such arrangement is shown in the present inventor's U.S. Pat. No. 4,784,581, where the discharge cylinder head is cut away in the area around the suction port to form a V-shaped notch. The discharge cylinder head still extends to the four corners of the valve plate, where it is secured by suitable bolts at the four corners to provide the necessary structural rigidity and support for the valve plate which is clamped between the discharge cylinder head and the cylinder block. The remaining portion of the V-shaped notch overlying the suction port is covered by a plastic suction cylinder head, which is held in place by a suitable bolt extending through the valve plate into the cylinder head and made integral with at least the base portion of the suction muffler. In order to avoid an excess of clamping forces around the bolt, the bolt rests against a bracket member, which also serves to clamp in place an oil suction tube extending down in the oil reservoir in the bottom of the compressor casing. This suction tube admits a small amount of oil into the suction chamber for lubrication of the suction valve in the interior of the compressor cylinder. By spacing the suction cylinder head away from the discharge cylinder head, thermal conduction of heat to the suction plenum is minimized, and it has been found that the presence of a suction plenum as large as possible directly over the suction port ensures minimum restriction of flow of the suction gases for maximum efficiency.
Another arrangement of a plastic suction muffler adapted to make direct connection to the valve plate and suction port is shown in European Patent Publication 195,486, published Sep. 24, 1986. In this case, the compressor is provided with a metal cylinder head including a discharge chamber and defining a U-shaped slot at the suction port. A plastic suction muffler is mounted below the cylinder head and has an extension or appendage which projects into the U-shaped slot to make connection to the suction port. A specially shaped spring clip is secured over a projecting post on the suction muffler appendage, and extends vertically over the suction muffler with resilient ends to press the muffler against the valve plate. The slot has overhanging portions on the metal cylinder head and projecting ears with bent tabs on the clip slide over these overhanging portions and make frictional gripping engagement to hold the entire suction muffler assembly in place on the compressor.